On the Crucial website there is a drop-down utility that allows you to find and select your specific motherboard in order to determine the correct RAM for it. I have usd it many times, but this week I got some RAM sticks that would not fit. It is a DDR2 board, but they sent DDR3 type sticks. I contacted Crucial. As usual, I received excellent customer support. They checked it, and sure enough, the utility brought up the incorrect type RAM sticks for them when they looked it up. They're correcting the error that their system made, but I must admit that I should have noticed the error on the final order...but I didn't.
This is not a complaint against Crucial or their products. It's just a notice that if you use their utility make sure that it detects the correct type of RAM slot....DDR2...DDR3 etc. If it doesn't, let them know.

That is why I use CPU-Z. It actually reads it off your Motherboard as to what kind of ram it uses. It will be able to tell the speed it can use and the max size you can us also.

Sites like Crucial just have a database that has the info stored. This is all good except for when human error comes into play. By that I mean when who ever inputted the data for that motherboard they selected the wrong type of RAM and therefor anyone that looks up that motherboard gets the wrong information.

Crucial has a utility that reads off of the board, too. But the board was on order and I wanted the RAM to be enroute as well.
Crucial knows about the issue now and is working on it.